1. Field of the Invention
The present invention relates to internal combustion engines in general and, more particularly, to an intake valve assembly of an internal combustion engine.
2. Description of the Prior Art
In a conventional internal combustion engine, intake and exhaust poppet valves regulate the gas exchange. A valve train (i.e. cams, drive gears and chains, rocker arms, push rods, lifters, etc.) regulate the poppet valves. Fixed valve timing of the poppet valves of the conventional internal combustion engine, and especially of the intake valve, represents a compromise between two conflicting design objectives: 1) maximum effective pressure within a cylinder, thus torque, at the most desirable points in a range of engine operating speeds, and 2) a highest possible power peak output. The higher the RPM at which maximum power occurs, and the wider the range of an engine operating speed, the less satisfactory will be the ultimate compromise. Large variations in the effective flow opening of the intake valve relative to the stroke (i.e., in design featuring more than two valves) will intensify this tendency.
In conventional four-stroke internal combustion engines, during the ending phase of the exhaust stroke, both intake and exhaust valves to the combustion chamber are kept open simultaneously for a certain period (known in the art as a valve overlap period, or simply a valve overlap) in order to increase exhaust efficiency of the engine. However, as a consequence of both valves being open simultaneously, part of the exhaust gas burnt in the combustion chamber is blown past the open intake valve and into an intake passage of the engine where the exhaust gas is mixed with the air-fuel mixture flowing through the intake passage. The exhaust gases impair ignition of the air-fuel mixture and therefore adversely affect the engine performance. The instability and accompanying inefficiency are particularly acute in the medium to low speed operational ranges of the engine and during idling of the engine.
Typically, a range of engine operating speeds includes a low engine speed range (low engine speeds) and a high engine speed range (high engine speeds). Generally, the low engine speed range is defined as a speed range from an idle speed to a midrange speed, and high engine speed is defined as a speed range from the midrange speed to a maximum engine speed. In other words, the low engine speed is the engine speed at or near the lower end of the operating speed range of the engine, while the high engine speed is the engine speed at or near the upper end of the operating speed range of the engine.
At the same time, growing demand for minimizing exhaust emissions and maximizing fuel economy means that a low idle speed and high low-end torque along with high specific output of an internal combustion engine are becoming increasingly important. These imperatives have led to the application of variable valve timing systems (especially for intake valves). However, this approach is complex and expensive, and takes away from durability of the internal combustion engine. Moreover, effectiveness of the variable valve timing systems that regulate the valve train is limited to a downstream efficiency of the poppet valve. The poppet valve is far from ideal. Even when the valve is open, a disk-shaped head of the poppet valve is directly in front of an intake port opening, where it sits directly in the way of the air or air/gas mixture flow stream. However, currently, the poppet valve is the only kind of valve that can operate in the severe environment of the internal combustion engine.
Thus, the intake valve assembly of the prior art, including but not limited to those discussed above, are susceptible to improvements that may enhance their performance and cost. The need therefore exists for intake valve assembly that is simple in design, compact in construction and cost effective in manufacturing, and, at the same time, provides both an improved low-end torque along with a high power output of the internal combustion engine.